With the recent spread of portable electronic equipment such as notebook computers, video camcorders, and personal digital assistances, nonaqueous secondary batteries having high voltage and high energy density have come to be used widely as a power source. From the concern for the environmental protection, electric-powered vehicles and hybrid-powered vehicles utilizing electric powder as a part of motive power have already been put to practical use.
Various additives for nonaqueous electrolyte have been proposed to provide nonaqueous secondary batteries with improved stability or electrical characteristics. Examples of such additives include 1,3-propane sultone (see Patent Literature 1 below), vinyl ethylene carbonate (see Patent Literature 2 below), vinylene carbonate (see Patent Literature 3 below), 1,3-propane sultone or butane sultone (see Patent Literature 4 below), vinylene carbonate (see Patent Literature 5 below), and vinyl ethylene carbonate (see Patent Literature 6 below). Among them, vinylene carbonate is widely used for its high effectiveness. These additive compounds are considered to form a stable film called a solid electrolyte interface (SEI) covering the surface of an anode, which film is expected to prevent reductive decomposition of an electrolyte.
The recent rise in the price of rare metals, such as cobalt and nickel, has rapidly boosted use and development of a cathode material containing a low-cost metal material, such as manganese or iron. A manganese-containing, lithium transition metal oxide is one of cathode materials of current interest for its excellent performance, such as capacity and power, in nonaqueous secondary batteries. It is known, however, that in a nonaqueous secondary battery having a manganese-containing lithium transition metal oxide as a cathode active material, manganese is liable to be eluted from the cathode to cause a side reaction, resulting in deterioration of battery performance, such as capacity and power.
To prevent elution of manganese from a cathode, various additives for a nonaqueous electrolyte have been proposed, including a disulfonic ester as disclosed, e.g., in Patent Literature 7 below. There has still been a demand for further improvements.